Rocket engines require propellants to be fed to them at very high pressures. This has historically been accomplished in two general ways: first, with the use of a pressurized fluid, such as high pressure helium; and second, with the use of a pump.
In the first way (i.e., a xe2x80x9cblowdownxe2x80x9d system), a pressurized fluid is added directly to the propellant tank and exerts a force on the propellant. Nitrogen and helium, both inert gases, pressurized to a pressure as high as 50,000 PSI, have been used successfully in the past. As they are inert, there need be no barrier (e.g., membrane or piston) placed between these pressurized fluids and the propellant. The problem with this method, however, is that the pressurized fluid also exerts a force on the propellant tank. Because of the extremely high pressures required of the pressurized fluid, the walls of the propellant tank must be thick enough to withstand the pressure. The propellant tank is therefore very heavy. Rockets employing the pressurized fluid must use a greater proportion of their thrust lifting this extra weight, and therefore they are not as efficient as rockets that do not require this added weight.
Historically, one way to solve the above weight problem is to employ the use of a pump. Pumps (e.g., reciprocating, centrifugal, or radial pumps) are generally very complex and expensive and require their own driving means, such as an engine. Further, the engine driving the pump burns a significant percentage of the total propellant. For small rocket engine systems, since a pump is too complicated, too heavy, and too expensive pressurized fluids are generally used to pressurize the propellant. However, for large rocket engine systems, pumps have the advantage that the walls of the propellant tank need not be thick, since there is little or no pressure in the tank. Therefore, the propellant tank is much lighter, and the added weight of the pump is more than offset by the reduction in propellant tank weight.
Another problem with both the blowdown and pump pressurizing systems is the pressure limitation. Current rocket engine combustion pressures are generally limited to 3,000 PSI or less, because most rocket engine turbopumps cannot create an outlet pressure higher than about 7,000 PSI, and because in most blowdown systems, pressurizing propellant tanks above around 1,000 PSI requires tanks whose wall thicknesses and weights are prohibitive.
U.S. Pat. No. 3,213,804 to Sobey (xe2x80x9cSobeyxe2x80x9d) discloses fluid pressure accumulators that are connected to sources of low and high pressure by means of butterfly valves. Essentially, the pressurized fluid exerts force on the propellant in small, designated containers. While the walls of these containers must be thick in order to withstand the high pressure of the pressurized fluid, the walls of the propellant tank need not be. Therefore, the total weight of the rocket engine system employing Sobey""s invention may be less than that of the previously discussed rocket engine system because these containers (fluid pressure accumulators) are small in comparison to the propellant tank.
U.S. Pat. No. 6,314,978 to Lanning, et al. (xe2x80x9cLanningxe2x80x9d) discloses a reciprocating feed system for fluids having storage tanks 1, 2, 3 that are similar in purpose to the fluid pressure accumulators disclosed in Sobey. Instead of valves 50, 52, 54 disclosed in Sobey, Lanning discloses four valves for each storage tank 1, 2, 3. For example, associated with storage tank 1 are: valve 13 between storage tank 1 and low pressure fluid 5; valve 16 between storage tank 1 and high pressure discharge 7; valve 20 between storage tank 1 and vent manifold 18; and valve 24 between storage tank 1 and pressurized gas supply 8. Each valve must be accurately and reliably controlled by a controller 11. Further, each valve may have associated with it a sensor 11a. 
A problem with Sobey""s invention, however, is its complicated use of valves. In order to reduce the weight of Sobey""s invention further, the sizes of the fluid pressure accumulators must decrease (thus reducing their weight). However, as they decrease, the rotation speed and precision of the butterfly valves must increase in order to accommodate the same propellant flow rate to the rocket engine. This places great stresses on the valves, and eventually a point is reached (in reducing the size of the fluid pressure accumulators) at which the valves cannot reliably rotate fast enough to provide the required timing.
Lanning has problems that are similar to the problems of Sobey. For example, Lanning requires a trade-off between reducing the size and weight of storage tanks 1, 2, 3, and increasing the speed, reliability, and working pressure of the valves. In other words, in order to reduce the size and weight of storage tanks 1, 2, 3, the valves must be able to reliably and accurately open and close at a faster rate. This puts great stresses on the valves. Further, the control system must be more complicated.
In a preferred embodiment, the present invention provides for pressurizer for pressurizing a fluid, comprising: a pressurant entrance configured for the introduction of a pressurant; a fluid entrance configured for the introduction of said fluid; a fluid exit configured for the expulsion of said fluid; and at least one transfer chamber movable in a cycle with respect to at least one of said pressurant entrance, said fluid entrance, and said fluid exit, wherein said pressurizer is configured so that for a portion of a cycle said pressurant exerts a force on said fluid inside said transfer chamber, and wherein said transfer chamber is configured to receive said pressurant via said pressurant entrance, receive said fluid via said fluid entrance, and expel said fluid via said fluid exit by the force exerted by said pressurant upon said fluid inside said transfer chamber.
In a preferred aspect, the pressurizer comprises at least three transfer chambers, configured so that while at least one transfer chamber is in fluid connection with said fluid entrance, at least one other transfer chamber is in fluid connection with said fluid exit and said pressurant entrance. In another preferred aspect, at least one transfer chamber comprises: a movable piston configured to substantially separate said pressurant from said fluid inside said transfer chamber; and a limiter configured to prevent said piston from moving beyond a certain point inside said transfer chamber. In another preferred aspect, the pressurizer further comprises: a motor configured to move said transfer chamber at a cycle speed; a sensor configured to sense a quantity of propellant inside said transfer chamber; and a controller connected to said sensor and said motor, configured to adjust said cycle speed at least as a function of said quantity sensed by said sensor.
In another preferred aspect, a cross sectional area of said transfer chamber is less than {fraction (1/10)} a cross sectional area of said fluid exit. In another preferred aspect, the pressurizer further comprises a rotatable spindle housing a plurality of transfer chambers, wherein, in a cross section of said spindle, a distance between corresponding points of two transfer chambers is less than xc2xd a maximum characteristic length of said fluid exit along a direction of rotation of said spindle. In another aspect, in a cross section of said spindle, a dimension of said transfer chamber along a path taken by said transfer chamber is less than a minimum distance between said pressurant entrance and said pressurant exit along a path taken by said transfer chamber. In another aspect, in a cross section of said spindle, a maximum characteristic length of said fluid exit along a direction of rotation of said spindle is less than xc2xd of a minimum distance between said pressurant entrance and said pressurant exit along a path taken by at least one transfer chamber.
In another preferred aspect, the pressurizer further comprises a pressurant exit configured for the expulsion of a pressurant exhaust, wherein said pressurizer is configured to be able to provide a continuous stream of said fluid from said fluid exit throughout at least one complete cycle at least when sqrt(xcex94pentrance)*(Aentrance) less than sqrt(xcex94pexit)*(Aexit), where xcex94pentrance is a pressure drop between said fluid entrance and said pressurant exit, Aentrance is a cross sectional area of said fluid entrance, xcex94pexit is a pressure drop between said pressurant entrance and said fluid exit, and Aexit is a cross sectional area of said fluid exit.
In another preferred aspect, a cross sectional area of said fluid exit is less than xc2xd a cross sectional area of said fluid entrance. In another preferred aspect, the pressurizer comprises a plurality of transfer chambers each having a dimension less than 1 mm.
In another preferred aspect, the pressurizer may further comprise a pressurant exit configured for the expulsion of a pressurant exhaust, wherein a cross sectional area of said fluid entrance (Aentrance) and a cross sectional area of said fluid exit (Aexit) are chosen so that sqrt(xcex94pentrance)*(Aentrance) is at least approximately sqrt(xcex94pexit)*(Aexit), where xcex94pentrance is a pressure drop between said fluid entrance and said pressurant exit, and xcex94pexit is a pressure drop between said pressurant entrance and said fluid exit.
In another preferred aspect, the pressurizer further comprises a rotatable spindle housing a plurality of transfer chambers, wherein said pressurizer is configured so that said spindle is rotated by an expansion of said pressurant. In another preferred aspect, said transfer chamber comprises at least one jet hole configured to provide a substantially continuous flow of said pressurant from said transfer chamber via said jet hole in a direction substantially opposite a direction of motion of said transfer chamber to provide an impulse reaction force to said transfer chamber.
In another preferred aspect, the pressurizer further comprises: a first rotatable spindle housing a plurality of said transfer chambers; a second pressurant entrance configured for the introduction of said pressurant; a second fluid entrance configured for the introduction of said fluid; a second fluid exit configured for the expulsion of said fluid; and a second rotatable spindle housing a plurality of second transfer chambers that are each movable in a cycle with respect to at least one of said second pressurant entrance, said second fluid entrance, and said second fluid exit, wherein each of said second transfer chambers is configured to receive said pressurant via said second pressurant entrance, receive said fluid via said second fluid entrance, and expel said fluid via said second fluid exit, and wherein said fluid entrance is connected to said second fluid exit.
In another preferred aspect, the pressurizer comprises at least one differential transfer chamber having a first region having a first cross sectional area and a second region having a second cross sectional area smaller than said first cross sectional area, wherein said differential transfer chamber further comprises a differential piston having a first piston portion having a first piston cross sectional area approximately equal to said first cross sectional area and a second piston portion having a second piston cross sectional area approximately equal to said second cross sectional area.
In another preferred aspect, the pressurizer further comprises: a pressurant exit configured for the expulsion of a pressurant exhaust; at least one pre-pressurization entrance between said pressurant entrance and said pressurant exit; and at least one depressurization exit, connected to said pre-pressurization entrance, between said pressurant entrance and said pressurant exit, wherein said pressurizer is configured so that, during a cycle, said transfer chamber sequentially receives said pressurant at a medium pressure via said pre-pressurization entrance, receives said pressurant at a high pressure via said pressurant entrance, expels said pressurant at another medium pressure via said depressurization exit, and expels said pressurant at a low pressure via said pressurant exit.
In another preferred aspect, said transfer chamber comprises: a piston configured to separate said pressurant from said propellant inside said transfer chamber; and a spring configured to provide a force on said piston relative to said transfer chamber. In another preferred aspect, the pressurizer further comprises: a rotatable spindle housing a plurality of transfer chambers; and a lubricant injector configured to inject a sealing lubricant between said pressurant entrance and said spindle.
In another preferred embodiment of the present invention, an impulse reaction engine system comprises: a pressurant container configured to contain a pressurant; a propellant container configured to contain a propellant; an impulse reaction engine configured to receive said propellant; and at least one transfer chamber movable in a cycle with respect to at least one of said pressurant container, said propellant container, and said engine, wherein said engine system is configured so that for a portion of a cycle said pressurant exerts a force on said propellant inside said transfer chamber, and wherein said transfer chamber is configured to receive said pressurant from said pressurant container, receive said propellant from said propellant container, and expel said propellant to said engine by the force exerted by said pressurant upon said propellant inside said transfer chamber.
In another preferred aspect, the impulse reaction engine system may further comprise a gas generator configured to generate said pressurant. The impulse reaction engine system may further comprise a heat exchanger configured to transfer heat from said pressurant generated by said gas generator to said propellant.
In another preferred aspect, the impulse reaction engine system may further comprise an engine conduit between said transfer chamber and said engine and a propellant conduit between said transfer chamber and said propellant container, wherein said system is configured to be able to provide a continuous stream of said propellant to said engine throughout at least one complete cycle at least when sqrt(xcex94pentrance)*(Aentrance) less than sqrt(xcex94pexit)*(Aexit), where xcex94pentrance is a pressure drop between said propellant container and a pressurant exhaust, Aentrance is a cross sectional area of said propellant conduit, xcex94pexit is a pressure drop between said pressurant container and said engine, and Aexit is a cross sectional area of said engine conduit.
In another preferred embodiment of the present invention, an impulse reaction engine system comprises: an impulse reaction engine configured to receive a propellant and further configured to generate a pressurant; and at least one transfer chamber connected to and movable in a cycle with respect to said engine, wherein said engine system is configured so that for a portion of a cycle said pressurant exerts a force on said propellant inside said transfer chamber, and wherein said transfer chamber is configured to receive said pressurant from said engine and expel said propellant to said engine by the force exerted by said pressurant upon said propellant inside said transfer chamber.
In another preferred aspect, the engine system comprises at least one differential transfer chamber having a first region having a first cross sectional area and a second region having a second cross sectional area smaller than said first cross sectional area, wherein said differential transfer chamber further comprises a differential piston having a first piston portion having a first piston cross sectional area approximately equal to said first cross sectional area and a second piston portion having a second piston cross sectional area approximately equal to said second cross sectional area. In another preferred aspect, the engine system may further comprise a propellant container configured to contain a propellant, wherein said transfer chamber is configured to receive said propellant from said propellant container. In another preferred aspect, said propellant may be in a gas state.
In another preferred aspect, said transfer chamber may comprise: a piston configured to separate said pressurant from said propellant inside said transfer chamber; and a spring configured to provide a force on said piston relative to said transfer chamber. In another preferred aspect, the engine system may further comprise a heat exchanger configured to transfer heat from said pressurant generated by said engine to said propellant.
In another preferred embodiment of the present invention, a fluid transport system for transferring fluid from a low pressure reservoir to an outlet at high pressure in a continuous stream comprises: a plurality of storage tanks, each of said storage tanks being capable of confining fluid at high pressure; draining means for draining fluid from each of said plurality of storage tanks in sequential order to said outlet, said draining means draining each of said plurality of tanks in sequence such that a continuous stream of fluid is supplied to said outlet at high pressure; and filling means for supplying fluid from said low pressure reservoir to each of said drained storage tanks in sequential order to fill said respective tanks with said fluid; said sequential order of each of said draining means and said filling means being out of phase with each other such that as one storage tank in said plurality is being drained by said draining means, at least another of said storage tanks is being filled by said filling means, wherein said draining means is configured to be able to be draining at least three storage tanks simultaneously.
In another preferred embodiment of the present invention, a fluid transport system for transferring fluid from a low pressure reservoir to an outlet at high pressure in a continuous stream comprises: a plurality of storage tanks, each of said storage tanks being capable of confining fluid at high pressure; draining means for draining fluid from each of said plurality of storage tanks in sequential order to said outlet, said draining means draining each of said plurality of tanks in sequence such that a continuous stream of fluid is supplied to said outlet at high pressure; and filling means for supplying fluid from said low pressure reservoir to each of said drained storage tanks in sequential order to fill said respective tanks with said fluid; said sequential order of each of said draining means and said filling means being out of phase with each other such that as one storage tank in said plurality is being drained by said draining means, at least another of said storage tanks is being filled by said filling means, wherein said system is configured so that a ratio of a number of storage tanks that are being filled by said filling means to a number of storage tanks that are simultaneously being drained by said draining means is at least three. In a preferred aspect, the fluid transport system may further comprise a pressurant having a pressurant pressure, wherein said ratio is set to be at least approximately a square root of a ratio of a pressure difference between said pressurant pressure and said high pressure to a pressure difference between said low pressure and ambient pressure.
In another preferred embodiment of the present invention, a fluid transport system for transferring fluid from a low pressure reservoir to an outlet at high pressure in a continuous stream comprises: a plurality of storage tanks, each of said storage tanks being capable of confining fluid at high pressure; draining means for draining fluid from each of said plurality of storage tanks in sequential order to said outlet, said draining means draining each of said plurality of tanks in sequence such that a continuous stream of fluid is supplied to said outlet at high pressure; and filling means for supplying fluid from said low pressure reservoir to each of said drained storage tanks in sequential order to fill said respective tanks with said fluid; said sequential order of each of said draining means and said filling means being out of phase with each other such that as one storage tank in said plurality is being drained by said draining means, at least another of said storage tanks is being filled by said filling means, wherein said fluid transport system comprises at least one differential differential storage tank having a first region having a first cross sectional area and a second region having a second cross sectional area smaller than said first cross sectional area, wherein said differential storage tank further comprises a differential piston, movable inside said differential storage tank, having a first piston portion having a first piston cross sectional area approximately equal to said first cross sectional area and a second piston portion having a second piston cross sectional area approximately equal to said second cross sectional area.